Power grid strength evaluation method, device, equipment, medium and product

Abstract

The invention discloses a power grid strength evaluation method and device, equipment, a medium and a product, and relates to the field of power system dynamic stability, and the method comprises the steps: building admittance and impedance models of all power supplies and network elements of a system in the impedance modeling process of the power system; the admittance and impedance model comprises a power supply admittance matrix, a power supply impedance matrix, a network node admittance matrix and a network node impedance matrix of all power supplies; based on the admittance and impedance model, establishing a whole-system closed-loop admittance matrix according to a closed-loop feedback relation between equivalent voltage disturbance and equivalent current disturbance of all buses; based on the closed-loop feedback relationship, defining a source network voltage interaction stability boundary representing the power grid strength according to the sensitivity of the system characteristic value to a source network voltage transfer function; and positioning a power grid strength weak area according to the source network voltage interaction stability boundary, and improving the power grid strength. According to the method, the oscillation risk caused by interaction of the control loops in the converter can be described.

Description

Technical Field

[0001] The present application relates to the field of dynamic stability of power systems, and in particular to a method, device, equipment, medium and product for evaluating the strength of a power grid. Background Art

[0002] Under the real threat of the gradual depletion of global fossil energy and the increasingly serious greenhouse effect, new energy represented by wind power and photovoltaics has been connected to the power grid on a large scale through power electronic equipment such as grid-connected inverters. The level of power electronics in the power grid has been continuously improved, and "high proportion of new energy" and "high proportion of power electronic equipment" have become the inevitable trend of the development of the power system.

[0003] The instability caused by multi-loop coupling of new energy grid-connected inverters greatly affects the strength of the system grid. Among the many indicators for evaluating system strength, the short circuit ratio (SCR) has received widespread attention. It was first used to analyze the strength of the receiving AC grid in AC / DC systems. When the short circuit ratio is applied to multi-infeed DC scenarios, it faces the problem of interaction between multi-infeed systems. The academic community has made many studies on this. The multi-infeed DC short circuit ratio (MISCR) proposed by the CIGRE DC Working Group is widely used. The relevant literature considers voltage interaction and uses a multi-port Thevenin equivalent circuit to obtain an improved multi-infeed short circuit ratio. Based on the system decoupling model, the DC loop outside the object to be studied is equivalent to the system impedance, thereby defining the multi-infeed critical short circuit ratio, and pointing out that the derived critical short circuit ratio is consistent with the voltage sensitivity factor. The feasibility of the method is proved through theoretical analysis and simulation verification.

[0004] The short-circuit ratio has been widely used to describe the strength of the system. However, the characteristics of the converter itself determine that its short-circuit current is naturally smaller than that of the synchronous motor. This makes the converter always classified as a relatively weak system under the traditional definition of the short-circuit ratio. In addition, most definitions of the short-circuit ratio are based on static characteristic analysis, which makes it difficult to examine the role of a large number of control systems associated with the grid connection of renewable energy. Therefore, it has limitations in describing the strength characteristics of high-proportion power electronic systems. In order to accurately and quickly evaluate the interaction of multi-infeed systems, the relevant literature proposed a method for calculating the multi-infeed interaction factor based on the reduced-order Jacobian matrix of the steady-state power flow equation, avoiding the errors caused by simulation analysis and analyzing the impact of different control methods and operating modes on the system strength. In addition, based on the boundary condition of static voltage stability, a site-dependent short circuit ratio (SDSCR) is proposed that takes into account the system interaction, which more accurately describes the grid strength of the multi-infeed system and can point out the weakest grid connection point of the renewable energy grid connection site.

[0005] The grid strength assessment of new energy power systems is a complex problem involving the interaction of multiple types of equipment and the coupling of multiple time scales. This shows that compared with traditional power systems, new power systems and grid strength analysis face many new challenges. Therefore, the study of grid strength assessment of new energy power systems with source-grid voltage interaction is an important and complex topic. In practice, it is often necessary to make a reasonable assessment of the system grid strength to guide the optimization of system parameters and the configuration of related equipment to ensure the safe and stable operation of the system. Therefore, it is necessary to propose indicators to describe the grid strength while ensuring accuracy and convenience, so as to quickly judge the stability of the system.

[0006] At present, the short-circuit ratio index is used to evaluate the strength of the system. First, it is necessary to know where the system is weak (positioning), and then improve it through some control methods. However, except for the generalized short-circuit ratio, the short-circuit ratio index system cannot reflect the oscillation risk caused by the internal control loop of the converter. Simply put, a weak system is prone to oscillation, and a strong system is not easy to oscillate, that is, the internal control loop of the converter has a considerable impact on the strength of the system. The short-circuit ratio index system cannot reflect these control interactions and cannot characterize the oscillation risk caused by the interaction of the various control loops inside the converter. The derivation of the generalized short-circuit ratio is complex and not conducive to engineering application. Summary of the invention

[0007] The purpose of this application is to provide a power grid strength assessment method, device, equipment, medium and product to solve the problem that the current short-circuit ratio index system cannot characterize the oscillation risk caused by the interaction of various control loops inside the converter.

[0008] To achieve the above objectives, this application provides the following solutions:

[0009] In a first aspect, the present application provides a method for evaluating power grid strength, comprising:

[0010] In the process of power system impedance modeling, the admittance and impedance models of all power sources and network elements of the system are constructed; the admittance and impedance models include the power admittance matrix, the power impedance matrix, the network node admittance matrix and the network node impedance matrix of all power sources;

[0011] Based on the admittance and impedance model, a closed-loop admittance matrix of the whole system is established according to the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses;

[0012] Based on the closed-loop feedback relationship, a source-grid voltage interaction stability boundary representing the strength of the power grid is defined according to the sensitivity of the system characteristic value to the source-grid voltage transfer function;

[0013] The weak area of ​​the power grid strength is located according to the source-grid voltage interactive stability boundary, and the power grid strength is improved.

[0014] In a second aspect, the present application provides a power grid strength assessment device, comprising:

[0015] An admittance and impedance model building module is used to build the admittance and impedance models of all power sources and network elements of the system during the impedance modeling process of the power system; the admittance and impedance model includes the power admittance matrix, power impedance matrix, network node admittance matrix and network node impedance matrix of all power sources;

[0016] A closed-loop admittance matrix establishment module for the whole system, used for establishing a closed-loop admittance matrix for the whole system based on the admittance and impedance model and according to the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses;

[0017] A source-grid voltage interactive stability boundary determination module is used to define a source-grid voltage interactive stability boundary representing the strength of the power grid based on the closed-loop feedback relationship and according to the sensitivity of the system characteristic value to the source-grid voltage transfer function;

[0018] The grid strength weak area positioning module is used to locate the grid strength weak area according to the source-grid voltage interactive stability boundary and improve the grid strength.

[0019] In a third aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement any of the above-described methods for assessing power grid strength.

[0020] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements any of the above-described methods for assessing the strength of a power grid.

[0021] In a fifth aspect, the present application provides a computer program product, including a computer program, which, when executed by a processor, implements any of the above-mentioned methods for assessing the strength of a power grid.

[0022] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0023] This application determines the power admittance matrix and its impedance matrix of all power sources in the power system impedance modeling process, the network node admittance matrix and its impedance matrix, and establishes a closed-loop admittance matrix of the whole system based on the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses to consider the admittance and impedance models of all power sources and network elements, and based on the closed-loop feedback relationship, defines the source-grid voltage interaction stability boundary that characterizes the strength of the power grid according to the sensitivity of the system eigenvalue to the source-grid voltage transfer function, so as to locate the weak areas of the power grid strength and improve the power grid strength. The power grid strength comprehensively reflects the interaction of all power sources and network elements, thereby characterizing the oscillation risk caused by the interaction of various control loops inside the converter.

[0024] Compared with the generalized short-circuit ratio, the derivation of the present application is simpler and more conducive to engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is an application environment diagram of a power grid strength assessment method in one embodiment of the present application;

[0027] Figure 2 A schematic diagram of small signal impedance modeling of the entire system provided in an embodiment of the present application;

[0028] Figure 3 A schematic diagram of a single grid-type inverter connected to an infinite system provided in an embodiment of the present application;

[0029] Figure 4 Schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Case 1-7; among them, Figure 4 (a) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 1, 2 and 3; Figure 4 (b) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 1, 4 and 5; Figure 4 (c) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 1, 6 and 7;

[0030] Figure 5 A schematic diagram of a single-grid inverter connected to an infinite system provided by another embodiment of the present application;

[0031] Figure 6 The diagram is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Case 8-14; among them, Figure 6 (a) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 8, 9 and 10; Figure 6 (b) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 8, 11 and 12; Figure 6 (c) is a schematic diagram of the system pole diagram, spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to Cases 8, 13 and 14;

[0032] Figure 7 A schematic diagram of a single-grid inverter connected to an infinite system provided by another embodiment of the present application;

[0033] Figure 8 Schematic diagram of the system pole diagram for Case 15-17.

[0034] Fig. 9 The following is a schematic diagram of the system spectrum diagram, voltage simulation waveform diagram, and frequency simulation waveform diagram corresponding to Case 15-17; among them, Fig. 9 (a) is a schematic diagram of a system spectrum diagram, a voltage simulation waveform diagram, and a frequency simulation waveform diagram corresponding to the grid-connected inverter 1 in Cases 15-17; Fig. 9 (b) is a schematic diagram of the system spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to the grid-type inverter 8 in Cases 15-17; Fig. 9 (c) is a schematic diagram of the system spectrum diagram, voltage simulation waveform diagram and frequency simulation waveform diagram corresponding to the grid-following inverter 3 in Case 15-17. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0037] The present application embodiment provides a method for evaluating the strength of a power grid. The method is executed by a computer device, and can be executed by a computer device such as a terminal or a server alone, or can be executed by a terminal and a server together. In the present application embodiment, Figure 1 As shown, the method includes the following steps.

[0038] S1: In the process of power system impedance modeling, the admittance and impedance models of all power sources and network elements of the system are constructed; the admittance and impedance models include the power admittance matrix, power impedance matrix, network node admittance matrix and network node impedance matrix of all power sources.

[0039] S2: Based on the admittance and impedance model, a closed-loop admittance matrix of the entire system is established according to the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses.

[0040] S3: Based on the closed-loop feedback relationship, a source-grid voltage interaction stability boundary representing the strength of the power grid is defined according to the sensitivity of the system characteristic value to the source-grid voltage transfer function.

[0041] S4: Locate the weak area of ​​the power grid strength according to the source-grid voltage interactive stability boundary, and improve the power grid strength.

[0042] In an exemplary embodiment, S1 is a process of establishing the admittance and impedance models of all power supplies and network elements of the system, wherein the impedance and admittance models of the power supplies can be derived from state equations and can also be obtained by fitting data of voltage and current measurements. It is worth noting that in the impedance modeling of a multi-machine power system, the impedance models of each power supply derived from the state equation need to be rotated to ensure that the coordinate systems of all power supplies are aligned.

[0043] The admittance of power source i connected to busbar i is Y si :

[0044]

[0045] Where n is the total number of system buses, Y sidd , Y sidq , Y siqd and Y siqq They are the four components of its dq axis, Z si Yes si The corresponding impedance.

[0046] The admittance matrix Y of all power supplies in the system can be obtained from each power supply impedance model: S :

[0047]

[0048] Among them, Y S ∈2n×2n represents the admittance matrix of all power sources in the system, Y S =Z S -1 . Z S∈2n×2n is the impedance matrix of all power sources in the system, and n is the number of system nodes.

[0049] Establish the network node admittance matrix Y for the power network N :

[0050]

[0051] Among them, Y Nij represents the mutual admittance element between buses i and j, Y Nii represents the self-admittance element of busbar i, is the node impedance matrix of the network.

[0052] In an exemplary embodiment, S2 is a process of establishing a closed-loop admittance matrix of the entire system, which can be replaced by the following steps.

[0053] ΔU i =[ΔU id , ΔU iq ] T is the voltage disturbance value of bus i, which includes two voltage disturbance value components of d and q axes, and T represents matrix transpose.

[0054] Therefore, the voltage disturbance value of all buses is ΔU N :

[0055] ΔU N =[ΔU1…ΔU i …ΔU n ] T (4)

[0056] For the power source i connected to the network bus i, consider the equivalent voltage disturbance source ΔU of the power source i caused by the disturbance on the grid side or source side. li =[ΔU lid ,ΔU liq ] T and the current disturbance ΔI li =[ΔI lid ,ΔI liq ] T .

[0057] Therefore, the equivalent voltage and current disturbances of all buses are ΔU L and ΔI L for:

[0058]

[0059] In addition, ΔU L and ΔI L The following closed-loop feedback relationship is satisfied:

[0060]

[0061] Where E is the identity matrix, Z S is the impedance matrix of all power sources, Y w is the closed-loop admittance matrix of the whole system.

[0062] In an exemplary embodiment, S3 may be replaced by the following steps.

[0063] S3.1: For any system eigenvalue, determine a first satisfying condition for the power source impedance matrix and the network node impedance matrix to take values ​​at the system eigenvalue.

[0064] S3.2: Based on the relationship between the impedance voltage drop of the power sources connected to all buses and the equivalent current disturbance, determine the relationship between the values ​​of the power source admittance matrix, the network node admittance matrix and the network node impedance matrix at the eigenvalues ​​of the system according to the first satisfying condition.

[0065] S3.3: Based on the arbitrary transfer function matrix, determine the eigenvalue sensitivity of the source-grid voltage interaction according to the relationship.

[0066] S3.4: Based on the eigenvalue sensitivity, determine the degree of interactive coupling between the source and grid power supplies at the bus k where the system eigenvalue is taken.

[0067] S3.5: Minimize the degree of mutual coupling of the power sources and determine the source-grid voltage mutual stability boundary representing the strength of the power grid.

[0068] Furthermore, because of the closed-loop feedback relationship shown in equation (6), the system eigenvalue corresponds to the matrix Y w The denominator of each element is zero, and the mth system eigenvalue λ m satisfy:

[0069] |Z S (λ m )+Z N (λ m )|=0 (7)

[0070] Formula (7) is the first satisfying condition, where || represents the calculation of the determinant, Z S (λ m ) and Z N (λ m ) are Z S and Z N At the eigenvalue λ m The value of .

[0071] For the admittance matrix of the power supply and network, the following equation holds:

[0072] |Y S (λm )+Y N (λ m )|=0 (8)

[0073] Among them, Y S (λ m ) and Y N (λ m ) are Y S and Y N At the eigenvalue λ m The value of .

[0074] Through the mathematical transformation of matrix multiplication operation, we can get:

[0075]

[0076] Therefore, it can be concluded that formula (7) is still valid.

[0077] Impedance voltage drop ΔU of all power supplies connected to the busbars S and ΔI L The relationship can be expressed as:

[0078] ΔU S =Z S ΔI L (10)

[0079] Substituting formula (6) into formula (10), we can obtain:

[0080]

[0081] In formula (11), ΔU L =(Z S +Z N )Y S ΔU S The interaction between the impedance voltage drop of the power source connected to the bus and the overall voltage drop of the system network is characterized.

[0082] From formula (7), the relationship between the values ​​of the power admittance matrix, the network node admittance matrix and the network node impedance matrix at the system eigenvalue can be obtained:

[0083] |[Z S (λ m )+Z N (λ m )]Y S (λ m )|=0 (12)

[0084] For any transfer function matrix H(s) of the system, its inverse matrix is ​​G(s) = H(s) -1 , if |H(λ m)|=0 holds, then:

[0085]

[0086] in, Denotes the eigenvalue λ for G(s) m Take the retained amount.

[0087] Formula (12) satisfies the conditions of formula (13), so we can get:

[0088]

[0089] Among them, Z s (s) and Y w (s) are the values ​​of the Laplace operator at s.

[0090] Formula (14) is the eigenvalue sensitivity of the source-grid voltage interaction. For the power grid-connected area of ​​bus k, expand formula (14) to obtain a term corresponding to bus k:

[0091]

[0092] Among them, Z Nkk and Y wkk Z N and Y w The kth diagonal term of Nkk (λ m ), Y wkk (λ m ) and Z sk (λ m ) are Z Nkk , Y wkk and Z sk At the eigenvalue λ i The value of Y sk (λ m ) and Z sk (λ m ) is the bus k power admittance Y sk and impedance Z sk In λ m The value at r kdd 、r kdq 、r kqd and r kqq These are the four components of the dq-axis eigenvalue sensitivity of the source-grid interaction at busbar k.

[0093] It is worth noting that equation (15) uses the sensitivity of the eigenvalue to the source-grid voltage transfer function matrix to locate the key source-grid interaction coupling region that affects system stability.

[0094] The eigenvalue sensitivity of the source-grid power interaction in formula (15) is essentially the partial derivative of the scalar with respect to the matrix, so it can be rewritten as:

[0095]

[0096] Since formula (16) has four components in the dq axis, the size of formula (16) is comprehensively measured by the Frobenius norm.

[0097]

[0098] Among them, || F represents the Frobenius norm.

[0099] When the system is disturbed, considering the conservativeness of system stability, |Δλ m | F The maximum value of can be taken as the eigenvalue λ m =σ m +jω m The distance from the imaginary axis, i.e. -σ m ; Among them, -σ m is m Negative value of the real part; ω m is m The imaginary part of .

[0100]

[0101] Among them, max|| F Represents the maximum possible value of the norm.

[0102] Formula (18) describes the m The degree of interactive coupling of the source-grid power supply at bus k is taken as the value. In order to fairly and fully compare all eigenvalues, the eigenvalue set λ of all eigenvalues ​​of the system is defined. The minimum value of the following equation (18) is the source-grid voltage interaction stability boundary (SGVB).

[0103]

[0104] in, Represents λ m Find the minimum value of the expression in the range of the system eigenvalue set λ, Δ{} is the perturbation amount of the expression; max||F is the maximum value of the norm; Represents Y wkk In λ m Take the retained amount.

[0105] SGVB kIt represents the interaction stability boundary between the inverter power connected to the system bus k and the equivalent power grid of bus k, and SGVB k It is a local small signal grid strength metric that reflects the source network stability margin near the system bus k area, so it can be used to evaluate the oscillation risk of different renewable energy station power sources in the system. k The larger the value, the lower the voltage sensitivity of the power supply and equivalent power grid at bus k, that is, the stronger the anti-interference ability of the local area, the greater the power grid strength and system stability margin. k It shows that some dominant oscillation modes of the system are insensitive to the voltage interaction coupling between the power equipment connected to bus k and the equivalent power grid, and the system can tolerate larger disturbances. k When it is a negative value, the system small signal is unstable.

[0106] SGVB k is an indicator of multi-feed devices, because SGVB k The admittance matrix Y of the whole system is w Derived from. w The admittance matrix Y of all power sources S and the network node impedance matrix Z N Obtained through closed-loop feedback, the eigenvalue of the system is expressed as the matrix Y w Each element in the denominator has a corresponding term, and the matrix Y w The molecules show the response of different positions and different busbars of the network to the oscillation mode. k Comprehensively reflects the interaction of all power devices and network components in the system.

[0107] In an exemplary embodiment, the SGVB k The larger the value of , the lower the voltage sensitivity of the power supply and equivalent power grid at bus k, the stronger the anti-interference ability of the local area where bus k is located, and the greater the power grid strength and system stability margin; conversely, the SGVB k The smaller the value of , the higher the voltage sensitivity of the power supply and the equivalent power grid at bus k, the weaker the anti-interference ability of the local area where bus k is located, and the smaller the power grid strength and system stability margin.

[0108] According to the definition of formula (19), SGVB k The calculation of SGVB requires traversing all eigenvalue ranges to find the minimum value. However, in fact, due to the different sensitivities of different buses and different power supplies to different oscillation modes, some buses and power supplies can only or easily be excited and observed in certain oscillation modes. Therefore, in the actual calculation of SGVB kIt is only necessary to find it within the range of some specific oscillation modes. First, high-frequency oscillations can usually be well damped by the line, and high-frequency oscillations are not easy to propagate in the network. Therefore, high-frequency oscillation modes are not taken into account. In the case analysis of this application, only oscillation modes below 200Hz are taken for calculation. Secondly, only those modes with low damping are easy to be excited to oscillate. These oscillation modes are usually reflected in the characteristic roots close to the imaginary axis in the system pole diagram and the admittance matrix Y of the whole system. w The corresponding diagonal element spectrum of the peak, so those oscillation modes with large damping, that is, far away from the imaginary axis, often do not need to be considered. This also greatly narrows the range of eigenvalue selection. k is the small signal grid strength indicator, SGVB k In practical applications, it needs to be established on multiple reliable working points or estimated through real-time online measurement.

[0109] SGVB is stabilized by source-network interaction k The numerical positioning of the weak area of ​​the system power grid strength and the guidance to improve the power grid strength at the system bus k. Compare the SGVB of formula (19) k The minimum value is the required grid strength index value. k The value indicates that the local area power grid strength at bus k is low. Check and adjust the control parameters of the inverter connected to bus k. k The numerical value of determines the degree of improvement of the local area power grid strength at bus k, judges whether the improvement measures are effective, and judges the performance of different improvement measures, so as to achieve the purpose of enhancing the small signal stability of the local system and the power grid strength.

[0110] The technical solution of the present application is described below with specific examples.

[0111] The small signal impedance modeling of the whole system is as follows Figure 2 As shown, 17 cases from three systems are used to illustrate the performance of the SGVB indicator, as shown in Tables 1 to 3. Among them, Cases 1-7 are comparative experiments of single grid-type inverters connected to infinite systems; Cases 8-14 are comparative experiments of single grid-type inverters connected to infinite systems; Cases 15-17 are comparative experiments of 14 busbar systems modified.

[0112] First, cases 1-7 of a single grid-type inverter connected to an infinite system illustrate that the indicator can reflect the small signal instability caused by the control parameters of the grid-type inverter and the weak grid. Second, cases 8-14 of a single grid-type inverter connected to an infinite system illustrate that the indicator can reflect the small signal instability caused by the control parameters of the grid-type inverter and the strong grid. Finally, cases 15-17 of the 14-bus system transformation illustrate the applicability of the indicator SGVB to larger-scale power systems and that it can fully capture the interactive coupling of the inverter power source through the grid. After a large number of simulation experiments, SGVB k =0.5 is preliminarily considered to be the standard for distinguishing the strength of the local area power grid of bus k.

[0113] Consider Figure 3 The single grid-connected inverter is connected to an infinite system. Where GFL represents the grid-connected inverter, PCC represents the common connection point, R g and L g are line resistance and inductance, U g is the grid voltage. P is the inverter output active power. Cases 1-7 are divided into 3 groups, and Case 1 is the basic case of each group. Cases 1, 2, and 3 only have grid impedance changes to illustrate that the grid strength index SGVB can reflect the instability of the grid-type inverter connected to the weak grid. Cases 1, 4, and 5 only have current loop bandwidth changes. Cases 1, 6, and 7 only have phase-locked loop bandwidth changes. The current loop bandwidth and phase-locked loop bandwidth change to illustrate that the grid strength index SGVB can reflect the instability caused by the inverter control loop at different time scales. The values ​​of the system change parameters and the grid strength index SGVB of each group are shown in Table 1.

[0114] Table 1 System variation parameters and SGVB values ​​for Cases 1-7

[0115]

[0116] The total system admittance element Y for three groups of different influencing factors in cases 1-7 wkk The d-axis dd-term spectrum diagram and system pole diagram are as follows Figure 3 As shown in the first and second rows of each group in . It can be seen that the system stability of Case 1 is the worst among Cases 1-7. The pole diagram of the Case 1 system has an oscillation mode very close to the imaginary axis, with a frequency of 30.31Hz. At the same time, the spectrum diagram has a large peak near 30.31Hz. ΔU and Δω represent the voltage and frequency changes of the inverter, respectively. At 0.1s, an active load step with an amplitude of 0.1pu appears at the grid-connected point of the grid-following inverter. The voltage and frequency responses of the inverter are shown in Figure 4The 3rd and 4th rows of each group in the table are shown in Figure 1. The blue curves in each group have large oscillations, while the yellow curves have small oscillations and are quickly calmed down. The simulation experiment waveform is consistent with the grid strength indicator SGVB value in Table 1, which reveals that SGVB can fully capture the voltage interaction dynamic coupling between the grid type source grid and the grid.

[0117] Consider Figure 5 The single grid-type inverter shown is connected to an infinite system. Among them, GFM represents the grid-type inverter, PCC represents the common connection point, R g and L g are line resistance and inductance, U g is the grid voltage. P is the inverter output active power. Cases 8-14 are divided into 3 groups, and Case 8 is the basic case of each group. In Cases 8, 9 and 10, only the grid impedance changes to illustrate that the grid strength index SGVB can reflect the instability of the grid-connected inverter connected to the strong grid. In Cases 8, 11 and 12, only the voltage loop bandwidth changes. In Cases 8, 13 and 14, only the synchronous loop droop coefficient changes. The voltage loop bandwidth and the synchronous loop droop coefficient change to illustrate that the grid strength index SGVB can reflect the instability caused by the inverter control loop at different time scales. The values ​​of the system change parameters and the grid strength index SGVB of each group are shown in Table 2.

[0118] Table 2 System variation parameters and SGVB values ​​for Case 8-14

[0119]

[0120] The total system admittance element Y of three groups of different influencing factors in Case 8-14 wkk The d-axis dd-term spectrum diagram and system pole diagram are as follows Figure 6 As shown in the first and second rows of each group in . It can be seen that the system stability of Case 8 is the worst among Cases 8-14. There is an oscillation mode close to the imaginary axis in the pole diagram of Case 8 system, and its frequency is 13.31Hz. At the same time, there is a large peak near 13.31Hz in the spectrum diagram. ΔU and Δω represent the voltage and frequency changes of the inverter respectively. At 0.1s, an active load step with an amplitude of 0.1pu appears at the grid-connected point of the grid-connected inverter. The voltage and frequency responses of the inverter are shown in Figure 6 The blue curves in each group have large oscillations, while the yellow curves have small oscillations and are quickly calmed down. The simulation experiment waveform is consistent with the grid strength index SGVB value in Table 2, which reveals that SGVB can fully capture the voltage interaction dynamic coupling between the grid-type source grids.

[0121] Consider Figure 7The 14-bus system shown in the modification, where the inverters connected to buses 1, 3 and 6 are grid-following inverters, and the inverters connected to buses 2 and 8 are grid-building inverters. As shown in cases 15-17 in Table 3, three different control parameter combinations of GFL1 and GFM8 are set, and the rest of the system parameters remain unchanged. Figure 8 The system pole diagram of Case 15-17 is given, and it can be seen that the system in Case 15 has an oscillation mode very close to the imaginary axis with a frequency of 33.08Hz. The element Y of the full system admittance matrix of Case 15-17 is w11 , Y w88 and Y w33 The dd item on the d axis is Fig. 9 As shown in the first row of , each of them has a large peak at 33.08Hz. The grid strength index SGVB values ​​of all inverters in the system in cases 15-17 are shown in Table 4.

[0122] Table 3 System change parameters for Cases 15-17

[0123]

[0124] Table 4 SGVB values ​​for cases 15-17

[0125]

[0126] Busbars 1, 8 and 3 increase their active loads by 0.1 pu at 0.1 s. Fig. 9 The voltage and frequency waveforms of GFL1, GFM8 and GFL3 are given in rows 2 and 3. As the control parameters are adjusted, the grid strength in the local area of ​​busbars 1 and 8 increases. Fig. 9 The yellow waveforms of GFL1 and GFM8 in (a) and (b) are effectively suppressed compared to the blue waveforms. Although the control parameters of GFL3 are not changed, Fig. 9 The voltage and frequency dynamic waveforms of GFL3 in (c) have also been greatly improved, which fully illustrates the complexity of the interaction and coupling of different power sources through the power grid. As shown in Table 4, the complex source-grid interaction and coupling can be captured by the power grid strength index, which fully demonstrates the effectiveness of the power grid strength index SGVB.

[0127] Based on the same inventive concept, the embodiment of the present application also provides a power grid strength assessment device for implementing the power grid strength assessment method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more power grid strength assessment device embodiments provided below can refer to the limitations of the power grid strength assessment method above, and will not be repeated here.

[0128] In an exemplary embodiment, a power grid strength assessment device is provided, comprising:

[0129] An admittance and impedance model building module is used to build the admittance and impedance models of all power sources and network elements of the system during the impedance modeling process of the power system; the admittance and impedance model includes the power admittance matrix, power impedance matrix, network node admittance matrix and network node impedance matrix of all power sources;

[0130] The module for establishing the closed-loop admittance matrix of the whole system is used to establish the closed-loop admittance matrix of the whole system based on the admittance and impedance model and the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses.

[0131] A source-grid voltage interactive stability boundary determination module is used to define a source-grid voltage interactive stability boundary that characterizes the strength of the power grid based on the closed-loop feedback relationship and according to the sensitivity of the system characteristic value to the source-grid voltage transfer function.

[0132] The grid strength weak area positioning module is used to locate the grid strength weak area according to the source-grid voltage interactive stability boundary and improve the grid strength.

[0133] This application considers the impact of the dynamic characteristics of different components in the system on the stability of the system, and effectively solves the problem of evaluating the strength of the power grid under the complex voltage interaction between the grid-connected inverter of new energy and the power network. This method is suitable for power systems with a high proportion of new energy, and according to the availability of the internal control details of the inverter, this method can be calculated in both model-driven and data-driven ways. The proposed method is simple to calculate and has good practical engineering application value, and can quickly and conveniently evaluate the strength of the power grid of a power system with a high proportion of new energy.

[0134] In an exemplary embodiment, a computer device is provided, which may be a server or a terminal. The computer device includes a processor, a memory, an input / output interface (I / O for short) and a communication interface. The processor, the memory and the input / output interface are connected via a system bus, and the communication interface is connected to the system bus via the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store power grid strength assessment data. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, a power grid strength assessment method is implemented.

[0135] In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the above method is implemented when the processor executes the computer program.

[0136] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, which implements the above method when executed by a processor.

[0137] In an exemplary embodiment, a computer program product is provided, including a computer program, which implements the above method when executed by a processor.

[0138] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ReadOnlyMemory, ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (Magnetoresistive RandomAccess Memory, MRAM), ferroelectric random access memory (Ferroelectric RandomAccess Memory, FRAM), phase change memory (Phase Change Memory, PCM), graphene memory, etc. Volatile memory can include random access memory (RandomAccess Memory, RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0139] In this application, all actions to obtain signals, information or data are carried out in compliance with the relevant data protection laws and policies of the country where they are located and with the authorization given by the owner of the corresponding device.

[0140] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0141] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0142] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for evaluating power grid strength, characterized in that: The power grid strength assessment method comprises: In the process of power system impedance modeling, the admittance and impedance models of all power sources and network elements of the system are constructed; the admittance and impedance models include the power admittance matrix, the power impedance matrix, the network node admittance matrix and the network node impedance matrix of all power sources; Based on the admittance and impedance model, a closed-loop admittance matrix of the whole system is established according to the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses; Based on the closed-loop feedback relationship, a source-grid voltage interaction stability boundary representing the strength of the power grid is defined according to the sensitivity of the system characteristic value to the source-grid voltage transfer function; The weak area of ​​the power grid strength is located according to the source-grid voltage interactive stability boundary, and the power grid strength is improved.

2. The power grid strength assessment method according to claim 1, characterized in that: Specifically include: The power admittance matrix Y S for: Among them, Y s1 is the admittance of power source 1 connected to busbar i; Y si Y is the admittance of power source i connected to bus i; sn is the admittance of power source n connected to bus n, where n is the total number of buses; The network node admittance matrix Y N for: Among them, Y N11 is the self-admittance element of bus 1; Y N1j is the mutual admittance element between bus 1 and bus j; Y N1j is the mutual admittance element between bus 1 and bus n; Y Ni1 is the mutual admittance element between busbar i and busbar 1; Y Nij is the mutual admittance element between busbars i and j; Y Nin is the mutual admittance element between busbar i and busbar n; Y Nn1 is the mutual admittance element between busbar n and busbar 1; Y Nnj is the mutual admittance element between busbars n and j; Y Nnn is the self-admittance element of busbar n.

3. The power grid strength assessment method according to claim 2, characterized in that: The closed-loop feedback relationship is: Among them, Y S =Z S -1 , Z S is the power supply impedance matrix; Z N is the network node impedance matrix; ΔU L is the equivalent voltage disturbance; ΔI L is the equivalent current disturbance; Y w is the closed-loop admittance matrix of the whole system.

4. The power grid strength assessment method according to claim 1, characterized in that: Based on the closed-loop feedback relationship, the source-grid voltage interaction stability boundary representing the strength of the power grid is defined according to the sensitivity of the system characteristic value to the source-grid voltage transfer function, specifically including: For any system eigenvalue, determining a first satisfying condition for the power source impedance matrix and the network node impedance matrix to take values ​​at the system eigenvalue; the system eigenvalue corresponds to a value where the denominator of each element of the closed-loop admittance matrix of the entire system is zero; Based on the relationship between the impedance voltage drop of the power supplies connected to all the buses and the equivalent current disturbance, determine the relationship between the values ​​of the power supply admittance matrix, the network node admittance matrix, and the network node impedance matrix at the system eigenvalues ​​according to the first satisfying condition; Based on an arbitrary transfer function square matrix, determining the eigenvalue sensitivity of the source-grid voltage interaction according to the relationship; Based on the eigenvalue sensitivity, determining the source-grid power supply interaction coupling degree at the bus k where the system eigenvalue is taken; The power source mutual coupling degree is minimized, and the source-grid voltage mutual stability boundary characterizing the power grid strength is determined.

5. The method for evaluating the strength of a power grid according to claim 4, characterized in that: The source-grid voltage interaction stability boundary characterizing the grid strength is: Among them, SGVB k is the source-grid voltage interaction stability boundary at bus k, that is, the grid strength at bus k; m is the mth system eigenvalue; λ is the set of system eigenvalues; Δ{} is the perturbation of the expression; Y sk (λ m ) and Z sk (λ m ) is the bus k power admittance Y sk and impedance Z sk In λ m The value at; max|| F is the maximum value of the norm; -σ m is m Negative value of the real part; Z Nkk (λ m ), Y wkk (s) and Z sk (λ m ) are Z Nkk , Y wkk and Z sk The value of Z at the system eigenvalue, Nkk and Y wkk Z N and Y w The kth diagonal item of ; T is the transpose; Res λm Y wkk (s) indicates Y wkk In λ m Take the remaining amount; || F is the Frobenius norm.

6. The method for evaluating the strength of a power grid according to claim 5, characterized in that: Locate the weak area of ​​the power grid strength according to the source-grid voltage interaction stability boundary and improve the power grid strength, specifically including: According to SGVB k The value of SGVB locates the weak area of ​​the power grid and improves the strength of the power grid; wherein, the SGVB k The larger the value of , the lower the voltage sensitivity of the power supply and equivalent power grid at bus k, the stronger the anti-interference ability of the local area where bus k is located, and the greater the power grid strength and system stability margin; conversely, the SGVB k The smaller the value of , the higher the voltage sensitivity of the power supply and the equivalent power grid at bus k, the weaker the anti-interference ability of the local area where bus k is located, and the smaller the power grid strength and system stability margin.

7. A power grid strength assessment device, characterized in that: The power grid strength assessment device comprises: An admittance and impedance model building module is used to build the admittance and impedance models of all power sources and network elements of the system during the impedance modeling process of the power system; the admittance and impedance model includes the power admittance matrix, power impedance matrix, network node admittance matrix and network node impedance matrix of all power sources; A closed-loop admittance matrix establishment module for the whole system, used for establishing a closed-loop admittance matrix for the whole system based on the admittance and impedance model and according to the closed-loop feedback relationship between the equivalent voltage disturbance and the equivalent current disturbance of all buses; A source-grid voltage interactive stability boundary determination module is used to define a source-grid voltage interactive stability boundary representing the strength of the power grid based on the closed-loop feedback relationship and according to the sensitivity of the system characteristic value to the source-grid voltage transfer function; The grid strength weak area positioning module is used to locate the grid strength weak area according to the source-grid voltage interactive stability boundary and improve the grid strength.

8. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the power grid strength assessment method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the power grid strength assessment method described in any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the power grid strength assessment method described in any one of claims 1 to 6 is implemented.

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